I have been making yogurt in a crockpot. I cook the milk until it reaches 170, then cool it to 109 for about 8 hours.

I want to plug the crock pot into a thermostat that has a probe, where I can set it to go on at a certain temperature and then go off when it reaches another.

I have no soldering equipment. I don't want to spend much money. I have already put a lighting rheostat into an electrical box, and spliced it with an electrical cord. I keep having to readjust it and it doesn't work well.

Crockpots don't seem to allow this due to minimal temperatures required for safety. I've looked at devices, but am not clear if they do what I want.

1) Is there such a device I can purchase "off the shelf"?
2) Can I build one? In which case, I'd want specific recommendations. If you say "find an x amp, y volt" that is just another search for me where I may not find what I want.

One of my favorite movie lines was from Philadelphia: "Explain it to me like I'm a five year old." I don't quite need this. I can do simple, safe wiring. I just want to know the devices I need that meet my requirements. One more thing. If I set it to 109, I guess I want it to go no lower or higher than about 3 or 4 degrees. I'd need a probe that can go into the pot and stay there 8-12 hours, and the ability to merely plug the unit into the thermostat.

crockpots / slow cookers have an internal thermostat - however it is not 'adjustable' and.... the low-med-high settings are not temperature related, they are how much / many of the heating elements are "on." basically, "do you want to start cooking with 100 watts, 300 watts, or 1000 watts?" some of the fancier models will, after they reach some mystically unspecified temperature, "drop back" from a high wattage setting to a lower wattage setting. their design incorporates how fast the slow cooker "loses" heat which means how much heat needs to be supplied and the oh btw thermostat is really just a safety feature to keep it from going up in flames.

older slow cookers held lower temps; then the gummymint decided we were all killing ourselfs by "contents" being in the 40-140'F range for too long. newer slow cookers run hotter, and a lot of people run hotter under the collar trying to use them.

a one-device, dumb and simple, no wiring, off-the-shelf, etc. involved doohickey that:
- heats to 170'F then
- 'resets' to hold 109'F
- for x hours
- with temps and time frames user adjustable....
does not exist.

a PLC with the appropriate sensors attached and an un-interruptable control and heating power supply would work - I'm thinking this is a bit more than you want to go into.....

there are simple plug in devices that have a remote sensing probe and will turn on and turn off to maintain a set temperature.

5yo explanation of terms:
a "line thermostat" means it will directly switch the electricity on/off to the target device. i.e. no "power relays" required. these line thermostats all have wattage restrictions - they will likely handle a slow cooker, but no - they cannot handle the wattage required to switch on/off New York City.

"probe" - the doo-hickey you stick in the pot to sense temperature. go for a copper tube; nothing braided/etc.

you might also want to consider automatic yogurt makers. they've been down this path.

crockpots / slow cookers have an internal thermostat - however it is not 'adjustable' and.... the low-med-high settings are not temperature related, they are how much / many of the heating elements are "on." basically, "do you want to start cooking with 100 watts, 300 watts, or 1000 watts?" some of the fancier models will, after they reach some mystically unspecified temperature, "drop back" from a high wattage setting to a lower wattage setting. their design incorporates how fast the slow cooker "loses" heat which means how much heat needs to be supplied and the oh btw thermostat is really just a safety feature to keep it from going up in flames.

older slow cookers held lower temps; then the gummymint decided we were all killing ourselfs by "contents" being in the 40-140'F range for too long. newer slow cookers run hotter, and a lot of people run hotter under the collar trying to use them.

a one-device, dumb and simple, no wiring, off-the-shelf, etc. involved doohickey that:
- heats to 170'F then
- 'resets' to hold 109'F
- for x hours
- with temps and time frames user adjustable....
does not exist.

a PLC with the appropriate sensors attached and an un-interruptable control and heating power supply would work - I'm thinking this is a bit more than you want to go into.....

there are simple plug in devices that have a remote sensing probe and will turn on and turn off to maintain a set temperature.

5yo explanation of terms:
a "line thermostat" means it will directly switch the electricity on/off to the target device. i.e. no "power relays" required. these line thermostats all have wattage restrictions - they will likely handle a slow cooker, but no - they cannot handle the wattage required to switch on/off New York City.

"probe" - the doo-hickey you stick in the pot to sense temperature. go for a copper tube; nothing braided/etc.

you might also want to consider automatic yogurt makers. they've been down this path.

Just been going through some of the archives as was at a loose end, great explanation, enjoyed the read and found it useful.